Aqueous compositions containing cationic quaternary ammonium compounds or imidazolinium compounds having at least one long chain hydrocarbyl group, or combinations of quaternary ammonium compounds with certain fatty amidotertiary amines in the form of a protonated complex are well recognized in the art to provide fabric softening benefits in a laundry rinse operation.
Achieving a commercially desirable viscosity in such fabric softening compositions has been the focus of much attention in the patent literature. The viscosity of a softening liquid is clearly an important factor for both the product manufacturer as well as the consumer. For the consumer, the cream-like quality of a fabric softening liquid is associated with concepts of softness and mildness. On the other hand, if a liquid product is unduly viscous, dispensing problems in the washing machine may result. Consequently, product acceptance by consumers is often dependent on the manufacturer being able to provide a desirable and stable product viscosity which allows convenient handling and pourability by the consumer.
U.S. Pat. No. 4,379,059 describes a process for the manufacture of a shear thinning fabric softener wherein the softening composition is thickened with polymeric thickeners, such as polyvinylacetate, polyacrylamide and mixtures of guar gum with xanthan gum.
EP 331237 describes an aqueous fabric conditioning composition comprising a fabric softener and a hydrophobically modified nonionic cellulose ether.
EP 385749 describes aqueous fabric conditioning compositions containing as a thickener a hydrophobically modified nonionic polymer having a hydrophobic backbone and at least two hydrophobic groups per molecule attached to the backbone. Described in particular are (i) copolymers of ethylene oxide and/or propylene oxide with small amounts of C.sub.8 -C.sub.24 side chains; (ii) hydrophobically modified poly(ethylene oxide and/or propylene oxide/urethanes); and (iii) alkyl substituted poly(vinyl) alcohols.
U.S. Pat. No. 5,310,851 describes polymeric thickeners which are polyurethanes. Among the intended applications for such polymeric thickening there are described latex paints and paper coating compositions. The use of the described polymers in a fabric finishing composition is said to promote softening effects (Col. 6, lines 40-42).
Notwithstanding the availability of numerous commercial thickeners for fabric softening liquid compositions, there remains a need in the art for a thickener capable of being efficaceous in highly concentrated fabric compositions as well as capable of maintaining its stability in low pH softening compositions which are acidified by mineral or polycarboxylic acids.